Shelf life or freshness indicators affixed to food, beverage, and other product packages are useful and beneficial to producers and the public. A common way of indicating the shelf life of a product is to print a "sell by" or "use by" date on the package containing the product. A disadvantage of this type of pre-calculated, shelf life indicator is that it takes no account of the actual conditions (temperature, humidity, etc) under which the product is stored. Further, the pre-calculated, printed shelf life indicator may be easily visually lost in circumstances in which a consumer merely glances at the product, especially if the packaging contains other eye-catching text and graphics.
It is an object of the present invention to provide an "active" indicator, which is also more readily visible to the user, and which more precisely reflects the effects of varying storage conditions.